Fluid circuit in a turbine engine

ABSTRACT

An assembly for a turbine engine having an oil circuit. The oil circuit includes an air/oil heat exchanger, a primary bypass pipe connecting an intake of the air/oil heat exchanger to an outlet of the air/oil heat exchanger and surrounding the air/oil heat exchanger so as to exchange heat with the air/oil heat exchanger. The oil circuit further includes and a secondary bypass pipe of the primary pipe connecting the upstream end of the primary bypass pipe to the downstream end of the primary bypass pipe. The oil circuit also includes at least one valve for controlling the passage of the flow of oil into the primary and secondary bypass pipes and means for controlling the opening of said at least one valve for a temperature lower than a threshold temperature.

The present invention relates to an oil circuit as well as to a turbineengine equipped with such an oil circuit.

Like all internal combustion engines, turbine engines, whether turbojetor turboprop engines, include moving parts that rub against other movingparts or against stationary parts.

In order not to break due to heating due to friction, the parts aresprayed with oil which makes it possible to limit (or contain) theirheating and, on the other hand, to lubricate them to facilitate thesliding of the parts one on top of the other.

The oil flows in a circuit 10 provided with heat exchangers, inparticular oil/air exchangers 12, as shown in FIG. 1, having a matrix14, in the form of a sinuous pipe shaped so as to achieve heat exchange,into which the oil from said parts is introduced and then cooled beforebeing injected again onto said parts.

When starting a turbine engine in cold conditions (e.g. with atemperature below 0° C.), the oil in the matrix 14 of the air/oilexchanger 12 (or exchangers if applicable) can be frozen, making heatexchange between oil and air difficult or impossible since the oilcannot circulate in the matrix 14 of the exchanger 12. It is thennecessary to preheat the matrix 14 of the air/oil heat exchanger 12beforehand.

For this purpose, it is known to provide the air/oil heat exchanger 12with a bypass pipe 16 used as a defrosting channel and surrounding thematrix 14 of the air/oil heat exchanger 12 in order to heat the frozenoil. This bypass pipe 16 is connected at its upstream end to the intake18 of the heat exchanger 12 and the outlet 20 of the heat exchanger 12.The oil circuit 10 also includes a valve 22 for controlling the oil flowin the bypass pipe 16 to allow oil to flow through the matrix 14 of theexchanger 12 only when the temperature is below a predeterminedthreshold. However, since the oil passage cross-section of the bypasspipe 16 is smaller than the oil passage cross-section in the air/oilheat exchanger, overpressure exists in the oil circuit when the matrix14 of the heat exchanger 12 is frozen. Overpressure induces a risk ofdamage to the oil circuit 10.

In order to reduce this overpressure, an obvious solution is to increasethe flow cross-section of the bypass pipe 16 in order to increase theflow rate without changing the operating pressure conditions of the feedpumps. However, for reasons of space requirements, an increase in thepassage cross-section of the bypass pipe 16 is not possible.

The invention more particularly aims at providing a simple, efficientand cost-effective solution to this problem.

To this end, the invention proposes an assembly for a turbine enginecomprising an oil circuit including an air/oil heat exchanger, a primarybypass pipe connecting an intake of the air/oil heat exchanger to anoutlet of the air/oil heat exchanger and surrounding the air/oil heatexchanger so as to exchange heat with the air/oil heat exchanger, and asecondary bypass pipe of the primary pipe connecting the upstream end ofthe primary bypass pipe to downstream of the primary bypass pipe, thecircuit also comprising at least one valve for controlling the passageof the flow of oil through the primary and secondary bypass pipes andmeans for controlling the opening of said at least one valve for atemperature below a threshold temperature.

According to the invention, the addition of a secondary bypass pipeallows part of the fluid to be bypassed from the primary bypass pipe,reducing the fluid pressure in the primary bypass pipe under coldoperating conditions. The combination of a valve for controlling theflow of oil through the primary and secondary bypass pipes and means forcontrolling the opening of the valve for a temperature above a thresholdtemperature makes it possible to operate the primary and secondarybypass pipes only under cold operating conditions, no oil flowcirculating through these pipes when the temperature is above thepredetermined threshold temperature.

As the pressure drop increases with the decrease in temperature due tothe increase in oil viscosity, it is understood that the addition of asecondary bypass pipe is particularly useful. However, this secondarypipe has little impact on the oil heating function of the air/oilexchanger through the primary pipe. For example, a 30% bypass of the oilflow rate from the primary bypass pipe to the secondary bypass pipeallows the same defrosting time to be maintained with the heatexchanger.

According to another characteristic of the invention, the assemblyincludes a single valve arranged at the outlet of the primary bypasspipe and downstream of the outlet of the secondary bypass pipe. It wouldof course be possible to have one valve for each of the primary andsecondary bypass pipes. However, this obviously complicates theassembly.

In another embodiment, the single valve could be located at the intakeof the primary bypass pipe and upstream of the intake of the secondarybypass pipe.

The control valve can be a valve that can adopt at least two positions,a first open position allowing oil to pass through and a second closedposition blocking the oil passage. In this way, the thresholdtemperature is, for example, of the order of 70° C.

In another embodiment, the control valve can be a unidirectional two-wayvalve that can adopt at least two positions, a first open positionallows oil to pass through the valve and a second closed position blocksthe oil passage through the valve, but also intermediate positions.

According to another characteristic of the invention, the secondarybypass pipe may be at least ten times shorter than the length of theprimary bypass pipe. Also, the circuit includes the secondary branchpipe which can have a diameter at least three times smaller than thediameter of the primary branch pipe.

Having a shorter secondary bypass pipe and/or a smaller diameter thanthe primary bypass pipe, according to the above-mentioned ratios, allowsa good flow distribution between the primary bypass pipe and thesecondary bypass pipe in order to lower the pressure drop in the primarypipe while ensuring proper defrosting of the heat exchanger.

In addition, a shorter secondary bypass pipe and/or a smaller diameteraccording to the above ratios prevents overpressure in the oil circuitwhen the oil exchanger matrix is frozen without having to increase thecross-section of the primary bypass pipe. This reduces the size and massof the primary bypass pipe.

A secondary bypass pipe with a shorter length will be preferred due tothe induced mass reduction. In addition, it is very advantageous whenthe intake and outlet are arranged in close proximity to each other. Thediameter of the secondary bypass pipe is thus adjusted according to thelength of the pipe to ensure a good distribution of the oil flow in theprimary and secondary bypass pipes.

The invention also relates to a turbine engine with an oil circuit asdescribed above, in which the oil/air heat exchanger radially delimits aflow surface of a secondary air flow radially outwards.

The invention will be better understood, and other details,characteristics and advantages of the invention will appear upon readingthe following description given by way of a non restrictive examplewhile referring to the appended drawings wherein:

FIG. 1 is a schematic representation of an oil circuit using theprevious technique already described above;

FIG. 2 is a schematic representation of an oil circuit according to theinvention, the valve being in an open position;

FIG. 3 is a schematic representation of an oil circuit according to theinvention, the valve being in a closed position;

FIG. 4 is a schematic view, in perspective, from downstream, of aturbine engine comprising a heat exchanger according to the invention;

FIG. 5 is a schematic cross-sectional view of the positioning of a heatexchanger, in one path of the turbine engine,

FIG. 6a is a schematic view of an assembly according to the invention;

FIG. 6b shows a cross-sectional view of the assembly in a radial plane.

FIG. 7 is a perspective schematic view in a radial cross-section, of theassembly of FIG. 6 a;

Reference is made to FIG. 2 which represents an oil circuit 24 accordingto the invention. In this description, the term exchanger refers to ameans that is capable of exchanging heat between two entities. Usually astructural housing surrounds the heat exchanging means, so that theassembly can be called a heat exchanger without the structural housingactively participating in the heat exchange. Thus, it is clear that theinvention also covers this type of product.

As shown in FIG. 2, the oil circuit 24 includes a primary bypass pipe 26identical to the bypass pipe 16 in FIG. 1 and a secondary bypass pipe 28that connects the upstream end of the primary bypass pipe 26 to thedownstream end of the primary bypass pipe 26. More specifically, theupstream end of the primary bypass pipe 26 and the upstream end of thesecondary bypass pipe 28 are connected to each other at the intake ofthe feed pipe 30 of the heat exchanger or more specifically of thematrix 33 of the heat exchanger 31.

The downstream end of the primary bypass pipe 26 is connected to theintake of a valve 22 the opening/closing of which is controlled bycontrol means 35 authorizing/blocking the flow of fluid through thevalve 22 for an oil temperature below a given threshold temperature, forexample 70° C. In a particular embodiment of the invention, the means ofcontrol of the valve are passive and are made of wax capable of varyingin volume according to the surrounding temperature. The volume variationof the wax within the valve allows the oil to selectively pass throughthe valve or block the oil flow upstream of the valve. The valve outlet22 is connected to an outlet pipe 34 of the heat exchanger matrix.

In an alternative embodiment (not shown), the valve 22 could be mountedupstream of the upstream end of the primary bypass pipe 26 so as toallow fluid to flow in the primary bypass pipe 26 for a temperaturebelow the threshold temperature and prohibit oil flow for a temperatureabove the threshold temperature, the oil flow being allowed in thesupply pipe 30 of the oil matrix regardless of the temperature. In thisconfiguration, the upstream end of the secondary bypass pipe 28 isconnected to the outlet of the valve 22 or downstream of the downstreamend of the primary bypass pipe 26.

In yet another embodiment of the invention, it would be possible to useone valve for each primary 26 and secondary 28 bypass pipe, the openingand closing of these valves being simultaneously controlled by thecontrol means.

In the embodiment of FIG. 2, the valve 22 is preferably an on-offunidirectional one-way valve with two positions, one of which allows oilto flow through the primary 26 and secondary 28 bypass pipes and theother prohibits flow through said pipes 26, 28. It would still bepossible to use a pilot operated valve with two ports and two positions.

The oil flow in the matrix 33 is represented by the solid pipe arrows inFIG. 2.

According to the invention, when the oil in the matrix 33 is frozen, theoil flows through the primary pipe 26 and the secondary pipe 28 asrepresented by the dotted arrows in FIGS. 2 and 3.

The dual oil flow in the primary pipe 26 and the secondary pipe 28increases the flow rate of the moving oil when the matrix 33 is frozen,reducing the overpressure in the oil circuit 24, particularly in theprimary pipe for a given oil flow in the supply pipe 34.

Preferably, the secondary pipe 28 has an oil passage cross-section lessthan or equal to the diameter of the oil passage cross-section of theprimary pipe 26 so that the oil flows mainly through the primary pipe 26and thus ensures that the matrix 33 is defrosted.

Similarly, it is understood that the secondary pipe should be as shortas possible to reduce the pressure drop in the primary pipe whileensuring proper defrosting. Thus, for example, the secondary pipe can bedefined by a length at least ten times shorter than that of the primarypipe, and/or a diameter three times smaller than the first pipe.

FIG. 4 shows a turbine engine 36 as seen from downstream (in thedirection of the air flow) comprising a blower wheel 38 and the air/oilheat exchanger 31 carried by an outer annular housing 40 of thesecondary air flow path (arrow A in FIG. 5). As is best seen in FIG. 5,the heat exchanger 31 is carried by the housing 40 and its matrix isarranged to form a radially outer flow surface of the secondary air flowof the turbine engine, i.e. the air flow bypassing the low and highpressure compressors, the combustion chamber and the high and lowpressure turbines.

In practice, it is understood that the air/oil heat exchanger 31 is inthe form of a ring arranged around the axis 42 of the turbine engine 36.

In the description, the term “secondary pipe” is to be understood asreferring to any fluid passage allowing oil to flow between the upstreamand downstream ends of the primary pipe.

Thus, in the heat exchanger described above, the secondary pipe can be asimple orifice provided in a wall separating the oil flowing in thesupply pipe 30 and the oil flowing in the downstream part of the primarypipe 33.

In one embodiment of the invention, the primary pipe has a diameter ofabout 12 mm and the secondary pipe is an orifice as indicated in theprevious paragraph and has a diameter of 5 mm.

The length of the primary pipe is, in one exemplary embodiment, aroundseveral metres.

FIG. 6a represents a set 44 according to the invention comprising ahousing formed by a first half ring 46 and a second half ring 48connected to each other by a central part 50. This assembly 44 includes,as described above, an oil circuit 24 and a heat exchange matrix 33 aswell as cooling fins 70 arranged on the radially inner face of the oilmatrix 33. The central part includes an oil intake 30 in the matrix 33,an oil outlet 34 of the matrix 33 and the unidirectional valve 22. Asdescribed above, the oil intake 30 also supplies the primary pipe 26 andthe secondary pipe 28 and the oil outlet 34 is connected to the outletof the unidirectional valve 22 or more generally to an outlet of thevalve 22.

The first half ring 46 comprises a first semi-circular pipe branch 46 aand a second semi-circular pipe branch 46 c connected to each other by aconnecting branch 46 b formed at the circumferential end opposite thecentral part 50 (FIG. 6b ). The first branch 46 a is formed upstream ofthe second branch 46 c and the connecting branch 46 b of the first halfring 46 extends substantially axially. The first branch 46 a, the secondbranch 46 c and the connecting branch 46 b together form a first part 52of the primary bypass pipe 26.

The second half ring 48 comprises a first semi-circular pipe branch 48 aand a second semi-circular pipe branch 48 c connected to each other by aconnecting branch 48 b formed at the circumferential end opposite thecentral part 50. The first branch 48 a is formed upstream of the secondbranch 48 c and the connecting branch 48 b extends substantiallyaxially. The first branch 48 a, the second branch 48 c and theconnecting branch 48 b of the second half ring 48 together form a secondpart 54 of the primary bypass pipe 26. The first part 52 of the primarybypass pipe and the second part 54 of the primary bypass pipe togetherfully define the primary bypass pipe 26.

More specifically, as shown in FIG. 7, the central part 50 carries thevalve 22 which includes a tubular body 54 in which a piston 56 isslidably mounted between a first support position on a seat 58 closingthe oil flow between the outlet 60 of the primary pipe 26 and the outlet34 of the matrix 33 and a second position in which the piston 56 isremote from the seat 58 and allows the oil flow. The piston 56 comprisesa first 56 a radially outer part sliding with a seal in the body andconnected by a rod 56 b to a head 56 c of the piston intended to rest onthe seat 58 or around the outlet opening 62. This head includes anannular chamfer 64 for the support on the periphery of the orifice 62.When the oil flows through the opening 60, it then flows through thepipe 66 to reach the outlet 34 of the oil matrix 33.

As shown in FIG. 7, the secondary pipe 28 connects the upstream end ofthe primary pipe 26 to the downstream end of the primary pipe 26. Thisfigure also shows the oil intake port 68 in the primary pipe 26, thisport 68 being connected to the oil intake 30 of the matrix 33.

The primary pipe 26 and the secondary pipe 28 are supplied through theoil intake 30 of the matrix 33. The oil in the primary pipe 26 and thesecondary pipe 28 then flows to the valve 22, which blocks the oil atthe outlet 60 of the primary pipe 26 or allows the oil to escape throughthe outlet 34 of the oil matrix 33.

The flow in the primary pipe 26 includes in particular, a flow in thefirst half ring 46 and then in the second half ring 48 before reachingthe valve 22. More specifically, the oil flows into the firstsemi-circular branch 46 a, then the connecting branch 46 b and finallythe second semi-circular branch 46 c of the first half ring 46. Once theoil is at the downstream end of the second semi-circular branch 46 c ofthe first half ring 46, the oil then flows into the second half ring 48at the second semi-circular branch 48 c, then at the connecting branch48 b and finally at the first semi-circular branch 48 a before reachingthe outlet 34 of the oil matrix 33 through the valve 22.

1. An assembly for a turbine engine, comprising an oil circuit includingan air/oil heat exchanger, a primary bypass pipe connecting an intake ofthe air/oil heat exchanger to an outlet of the air/oil heat exchangerand surrounding the air/oil heat exchanger so as to exchange heat withthe air/oil heat exchanger and a secondary bypass pipe of the primarypipe connecting the upstream end of the primary bypass pipe to thedownstream end of the primary bypass pipe, the circuit also comprisingat least one valve for controlling the passage of the flow of oil intothe primary and secondary bypass pipes and means for controlling theopening of said at least one valve for a temperature lower than athreshold temperature, said secondary bypass pipe having a length atleast ten times shorter than the length of the primary bypass pipe. 2.The assembly according to claim 1, wherein the circuit includes a singlevalve arranged at the outlet of the primary bypass pipe and downstreamof the outlet of the secondary bypass pipe.
 3. The assembly according toone of claim 1, wherein the control valve is a valve capable of adoptingat least two positions, a first open position of which allows thepassage of oil and a second closed position blocks the passage of oilthrough the valve.
 4. The assembly according to claim 1, wherein thethreshold temperature is 70° C.
 5. The assembly according to claim 1,wherein the control valve is a unidirectional two-way valve.
 6. Theassembly according to claim 1, wherein the secondary bypass pipe has adiameter at least three times smaller than the diameter of the primarybypass pipe.
 7. A turbine engine comprising the assembly according toclaim 1, wherein the oil/air heat exchanger radially outwardly delimitsa discharge surface of a secondary air flow.